1. Field of the Invention
The present invention relates to a battery pack and a method for producing it in which the volume of an outer package part is suppressed as much as possible.
2. Description of the Related Art
In recent years, a demand for an information device such as a note book type personal computer, a mobile communication device such as a portable telephone and a portable electronic device such as a video camera has been rapidly increased. As a power source of such electronic devices, a sealed type small secondary battery such as a nickel-cadmium battery, a nickel-metal hydride battery, a lithium-ion battery has been frequently employed. The characteristics of the lithium-ion secondary battery such as high voltage, high energy density and lightweight have been made a good use of among them, so that the lithium-ion battery has been employed in a variety of fields.
Especially, to cope with the leakage of liquid which causes a problem when liquid type electrolyte solution is used, for instance, a battery using a gel polymer film obtained by impregnating polymer with non-aqueous electrolyte solution as an electrolyte, or what is called a polymer lithium-ion secondary battery using a completely solid state electrolyte are proposed.
In the above-described battery, as shown in FIG. 1, a single cell 301 formed by laminating battery elements is ordinarily housed in a pair of upper and lower plastic cases 303 and 304 together with a connecting board 302 having a protective circuit or terminals to obtain a battery pack 300 (for instance, see Japanese Patent Application Laid-Open No. 2002-8606).
However, in the above-described structure, the thickness of the plastic cases 303 and 304 needs to be 0.3 to 0.4 mm. Further, when a double side tape or a tolerance for fixing is taken into consideration, the thickness of about 0.8 to 1 mm is increased to the thickness of the battery. In an outer peripheral direction, a configuration for performing an ultrasonic welding to the upper and lower plastic cases 303 and 304 is needed. Accordingly, the thickness of about 0.7 mm is required therefor. Therefore, the battery pack 300 needs to increase its volume about 1.3 to 1.4 times as much as the battery.